Polyethylene (PE) as a kind of common plastics with excellent mechanical properties, electrical insulation, chemical corrosion resistance and low temperature resistance, widely used in industry, agriculture, automotive, communications and all areas of daily life. These excellent performances of polyethylene have close relation with the products and the catalyst. Phillips chromium catalyst, with producing about 40% high density polyethylene in the world, due to its product chain with a small amount of long branches, thus has unique rheology and processing performance, especially suitable for processing large hollow container, long-term static pressure gas pipe and resistance to water pipe, tank car, etc., and these products are still cannot be produce by Ziegler-Natta catalyst, after new metallocene catalyst and transition metal catalyst of polyolefin products. Phillips catalyst already has a very important position in the industrial production of polyolefin.
Phillips catalyst was first made by Phillips petroleum company's J. Hogan and R. L. Bank two researchers reported in the U.S. Pat. No. 2,825,721. The patent with chrome oxide as raw materials, under different conditions is studied, including polymerization temperature, polymerization time, monomer concentration, and the ratio of the catalyst, the chromium load of the catalyst, the carrier of modified, catalyst preparation conditions, such as effect on the properties of Phillips catalyst in olefin polymerization. Later, U.S. Pat. No. 4,295,997, U.S. Pat. No. 4,528,338, U.S. Pat. No. 5,401,820 developed Phillips catalysts, such as the low toxicity of chromic salt as raw materials, to avoid the use of high toxic CrO3 raw material.
Traditional department of vanadium catalysts used in homogeneous Ziegler-Natta catalyst for ethylene polymerization system, mainly used for adjusting the Ziegler-Natta catalyst product molecular weight distribution and the distribution of copolymerization monomer, to improve product performance, displays in: the production of polymer molecular weight distribution is narrow and high molecular weight; Production of ethylene/a-olefin copolymer, and copolymerization monomer insertion is more; Also can synthesize syndiotactic polypropylene, etc. Zakharov, examines the preparation of catalyst VCl4 load on MgCl2 carrier aggregation performance, found that the catalyst can produce wide molecular weight distribution of polyethylene, and response to hydrogen has a high value, can see literature Chinese Journal of Polymer Science, 2008, 26, 553-559. U.S. Pat. No. 4,199,475 reported four ethyl ester titanate and vanadium oxychloride load on the silica gel preparation of catalyst, has the very high activity of ethylene polymerization.
Due to Phillips catalysts are highly sensitive to changes in carrier form, so by changing the carrier or carrier of type, in the production of liquid oligomer and low molecular weight wax or ultra-high molecular weight polyethylene (UHMWPE), the molecular weight distribution of their products can be control in large scope. Two common characteristics of the second generation of Phillips catalyst is: 1) based on the carrier surface modification to the preparation of catalyst and polyethylene products with a new performance; 2) and chrome is the only active component of modified Phillips catalysts. The second generation of Phillips catalyst carrier of modification methods include: titanium dioxide modified, magnesium hydroxide, fluorine modification, modification, alkali modification, boron modified alumina, etc. At present, the second generation of modified Phillips catalyst has been used to produce all kinds of commercial use of different levels of polymer.
Among them, the carrier of catalyst after modified titanium dioxide, can significantly enhance the activity of chromium, shorten the induction time, improve the activity of catalyst polymerization and chain termination rate, reduce the average molecular weight of polymer, it is often beneficial for polymerization. Phillips Company R.D ietz (U.S. Pat. No. 3,887,494), b. Horvath (U.S. Pat. No. 3,622,521) and Chemplex Company of t. Pullukat (U.S. Pat. No. 378,001) conducted the research, the carrier used in the two companies respectively the Grace Davison series and now the PQ Company production of polyolefin special silica gel carrier. Introduction of titanium dioxide means there are two main types, one is titanium and silicon in the form of total gel (co-gel) deposition after forming, Ti content on the surface of the vehicle body and fairly; Is a kind of titanium dioxide coated on the molded silicone carrier, the titanium dioxide are mainly distributed in the surface of the carrier. Literature can see Journal of Catalysis, 1983, 118-126.
Among them, the fluorine modified with surface fluorine modified agent such as six ammonium fluosilicate reaction with silicon hydroxyl groups on the surface of the release of water, at the same time in the silicone surface Si—F keys. Modified silica gel on the surface of the electronegativity stronger F causes the surrounding atoms on the electron transfer, thereby weakening the silicon hydroxyl bond, thus increased the acid on the surface of the silica gel, literature can see Journal of Catalysis, 2 (2), 145, 1963. Rebenstrof and others without modification and after F the two Phillips catalysts of Fourier infrared spectrum characterization, found F modification of catalyst surface hydroxyl silicon stretching vibration peak (3746 cm-1) strength decreased obviously, show that F is helpful to remove silicon hydroxyl groups on the surface of the silica gel. In addition the author thinks that is still under 800° C. removal of OH groups on the linked Si atoms don't F atomic bonding, at the same time. Later, using the low temperature CO IR characterization, found that after six surface modification of ammonium fluosilicate, Cr atoms surrounding electron cloud density is reduced, at the same time, the distribution of the active center is improved, related literature can see Journal of Molecular Catalysis, 66 (1), 59, 1991.
Hogan points out an early patent Phillips catalysts of fluorine modification can adopt the following two ways: (1) to have been dry Phillips catalysts in direct mixed with (NH4)2SiF6; (2) the (NH4)2SiF6 and CrO3 solution were impregnated in the surface of silica gel. Aggregate results show that both ethylene homopolymerization reaction, or ethylene and propylene, 1-butylene, 1-octene, 1-pentene, alpha olefin copolymerization reaction, such as total impregnation method of fluorine modification of catalyst higher catalytic activity than powder mixing method. When using silica gel-fluoride as carrier, as the system of six ammonium fluosilicate join quantity from 0.5 wt. % higher to 3.5 wt. %, apparent polymerization activity showed a rising trend, and the introduction of fluorine on the regulation of the density of product has obvious effect, showed that fluoride can promote a monomer insertion reactions. Kallenbach (U.S. Pat. No. 3,445,367, 1969) using the direct dry mixing method to four different fluoride compounds (NH4)2SiF6, CuSiF6, NH4BF6 and CuBF6 on modification, Phillips catalyst compared to the traditional Phillips catalyst, these F modified catalysts are able to produce relatively narrower molecular weight distribution of HDPE.
McDaniel the original silicone impregnated in (NH4)2SiF6 solution, respectively in 420, 650 and 420° C. after three temperature roasting, treated with this kind of fluorinated silicone impregnated with CrO3CH3CN solution, the final will be a catalyst for high temperature activation in the air. Researchers at different calcination temperature on different activation, F content in the catalyst samples found after fluorine modification of catalyst, the Cr(VI) of saturated load reduced. Under the same calcination temperature, Cr(VI) the biggest load with the increase of load F fell sharply, and the sample of the 870° C. fell the most, it shows that high temperature fluoride could accelerate sintering silica gel. Literature can see Journal of Catalysis, 76 (1), 37, 1982.
At present, there is no related load type vanadium oxide as olefin polymerization active center reported that no load type used as catalyst for the active component is introduced into Phillips chrome vanadium oxide reports; Also about modification of TiO2 or no fluorine modified load type chrome vanadium metal oxide double polyethylene catalyst activity center, the present invention that the load type chrome vanadium metal oxide double polyethylene catalyst active sites on the basis of further introduce the modified titanium dioxide or fluorine components.